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Search forPoor weather keep basking sharks away
Friday, October 24, 2008, 12:15
The SeaWatch SW survey team this year recorded 297 basking shark sightings off Gwennap Head, near Land's End in Cornwall. But for the second year in a row, few were seen in July and numbers peaked in September.
As the second largest of the world's fish, after the whale shark, the basking shark grows up to 30 feet long, and is usually a major attraction for visitors to the Westcountry during the midsummer holiday period. The typical pattern sees shark sightings peak between May and July, and decline sharply after August.
Project co-ordinator Dr Russell Wynn of the National Oceanography Centre, Southampton, believes the change is related to shifts in the distribution and abundance of the sharks' favourite food, tiny planktonic shrimps called copepods.
Dr Wynn said: "Copepods are normally concentrated at the surface in coastal waters during late spring and summer. However, windy unsettled weather during the last two summers has mixed up the surface waters, preventing formation of dense plankton concentrations. This means the sharks have gone elsewhere to find food or have stayed below the surface."
Dr Wynn said: "The peak count of sharks seen off Gwennap Head was particularly late, with 26 seen on September 19.
"In the last two years, the weather has actually settled down during September. This has encouraged a late plankton bloom, and has seen sharks appearing again in good numbers during the autumn.
"From a scientific point of view, we're now hoping next summer is a scorcher, so that we can compare results with the previous two years."
The SeaWatch SW survey involves volunteer observers recording marine wildlife at a series of watch points around the Westcountry. The focal point is Gwennap Head, which is monitored from dawn to dusk every day between July 15 and October 15. The survey is due to run until at least 2011 to assess long-term wildlife trends.
In addition to basking sharks, for the second successive year there were more than 1,000 sightings of the Balearic shearwater, a globally endangered seabird with a total population of just 2,500 breeding pairs.
The survey team also recorded more minke whales, bottlenose dolphins, ocean sunfish and puffins than in 2007, but fewer common dolphins and kittiwakes.
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